Portion of a shoe midsole



FIG. 1 is a front view of a portion of a shoe midsole showing my new design;

FIG. 2 is a rear perspective thereof; and,

FIG. 3 is a side view thereof.

The broken lines immediately adjacent to the shaded areas represent unclaimed boundaries of the design. The broken line showing of the remainder of the shoe is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a portion of a shoe midsole, as shown and described. 